The invention relates to a magnetoelastic force-measuring device of the type comprising a metallic annular thrust body of low elastomechanical hysteresis with magnetostrictive properties, which has mutually parallel end faces subjectable to the force to be measured, and bears a coaxially arranged exciting and measuring winding.
There is known a magnetoelastic force-measuring device according to the generic concept (German Offenlegungsschrift No. 2,365,937), in which the annular thrust body is constructed as a solid ring and has channels which connect its opposite faces with each other and through which the winding is run. If the end faces of the ring, which, for example, can consist of normal steel, magnet steel or ferrite, are subjected hereby to the compressive force to be measured, the change that thereby results in the permeability of the magnetostrictive material of the ring leads to a change in the alternating-current resistance in the winding excited by alternating current, which is a measure for the compressive force acting on the end faces.
Moreover, it is generally known (the German journal: Technisches Messen tm, vol. 5/1985, pages 189 to 198, especially page 192 et seq.), to use magnetoelastic sensors for measuring torques in shafts or as force sensors.
It is an object of the invention to construct a simple magnetoelastic force-measuring device in such a way that a good thermal error compensation is guaranteed in conjunction with a high measuring sensitivity.
Moreover, the device is also to be suitable for non-stop operation under difficult physical and chemical environmental conditions.
This object is achieved with a generic force-measuring device according to the invention by providing an arrangement wherein a metallic sleeved tension body is arranged to fit coaxially in the annular thrust body, said sleeved tension body being likewise of low elastomechanical hysteresis and with magnetostrictive properties and being supported at its one end with an annular flange on the free end face of the annular thrust body which is not supported against an abutment, the other free end being provided with a receiver for introducing the force, wherein the magnetostrictive properties are formed by a thin, homogeneous, uniform, soft-magnetic measuring film, which is applied, on the one hand, to the outer lateral surface of the annular thrust body and, on the other hand, to the inner lateral surface of the sleeved tension body, wherein the exciting and measuring winding of the annular thrust body is constructed as a ring coil, and is arranged on the measuring film on the outer lateral surface of the annular thrust body, and wherein, in its interior, the sleeved tension body likewise bears a ring coil constructed as an exciting and measuring winding, which ring coil is arranged on the measuring film on the inner lateral surface of the sleeved tension body, the two ring coils being connected up to make an inductive half-bridge and being capable of being connected to an electronic apparatus for exciting and evaluating the differential inductance.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.